The Australian government announced plans on Tuesday to release just under 20% of children kept in immigration detention centres, following criticism from human rights advocates that detaining minors in such conditions is tantamount to ‘child abuse.’

However, the government is standing by its hardline, and much-criticised, immigration policies. It will grant freedom to around 150 of the 876 children currently held in detention centres on the Australian mainland and on remote islands. Children under the age of 10 and their families will be given priority.

Immigration Minister Scott Morrison said children and their families in centres on the mainland who arrived before the introduction of tough new laws in mid-2013 would be released into the community on bridging visas while their applications for asylum are processed. He said this would happen by the end of the year.

Minors being held in offshore detention centres and those born in Australia to asylum seekers since a cut-off date of July 19 would be excluded, however.

Morrison said the exclusion was critical to Australia’s success in stopping asylum seekers from attempting the perilous boat journey, often made by people fleeing conflict zones after paying people-smugglers in Indonesia.

“Offshore processing is one of the measures stopping the boats and I don’t think encouraging children to get on boats where they can die at sea is an acceptable humanitarian outcome,” Morrison told reporters.

“This government won’t be watering down its policies on border protection that are saving lives at sea.”

Conservative Prime Minister Tony Abbott won an election last September after campaigning heavily on tough immigration policies, which have been criticised internationally but which polls show remain popular with voters.

A group of prominent Christian leaders has accused Morrison of committing “state-sanctioned child abuse” with the government’s tough border security measures, while the United Nations has warned Australia could be violating its obligations as a signatory to UN refugee conventions.

The number of children still held in detention centres is down from a peak of 2,000 last July, Morrison said.

More than 500 are on the mainland, of whom 150 will be eligible for release. The 148 children on Christmas Island, an Australian territory in the Indian Ocean, and 193 children on the South Pacific island of Nauru will not be released.

A further 1,547 children held in mainland community detention centres will be looked at case by case, Morrison said.

The cut-off date of July 19 marks the introduction last year by the former Labor government of rules that meant all new boat arrivals would be sent offshore for processing.

Abbott’s government toughened that further with a secretive policy of turning back boats at sea. It also wants to ban permanent visas for anyone who arrived in Australia by boat.

Prior to the government's introduction of its tough border security policies, boats were arriving almost daily, with hundreds of people dying en route.

Since last December, only one boatload of asylum-seekers has managed to reach the Australian mainland.

Reports of children with mental and physical health issues

Law firm Maurice Blackburn, which represents 94 babies born in detention to people who arrived since July 19, said all children in detention should be included in the release plans.

It said Christmas Island and Nauru did not have basic medical and health services.

A former doctor at Nauru told the HRC inquiry last month that the government asked him to cover up evidence that children held in the camps were suffering from widespread mental illness caused by their confinement.

Children on Nauru include around 50 minors who are among a group of 157 Tamil Sri Lankan asylum seekers who are at the centre of a High Court challenge over the government’s authority to detain asylum seekers on the high seas and send them to another country.

“We have heard stories of children with teeth abscesses or teeth cavities that have gone untreated for months,” Maurice Blackburn lawyer Jacob Varghese said. “We know of children with grave psychological problems.”

“Today’s announcement needs to go much further - no child should be living in detention,” he said.